Set Appliance State:

Mains Power Off
Observe the manual pressure gauge on the underside of the appliance

Observation:

Increase the system pressure slightly while observing the gauge, the gauge should respond to the increase in system pressure.
Does the pressure gauge respond to the increase in system pressure?
Note:
Ensure the system pressure is correctly set at between 1 and 1.5 bar when the appliance and system are cold before moving onto next test.